添加收藏夹，只运行一次的javascript代码

function get_cookie(Name)
{
var search = Name + "="
var returnvalue = "";
if (document.cookie.length > 0)
{
var offset = document.cookie.indexOf(search)
if (offset != -1)
{
offset += search.length
end = document.cookie.indexOf(";", offset);
if (end == -1)
end = document.cookie.length;

returnvalue=unescape(document.cookie.substring(offset, end))
}
}
return returnvalue;
}

function WindowClose()
{
var s = get_cookie('bookmarkit')
alert(s)
if (s=='')
{
if( confirm("感谢您访问本网站。您愿意收藏天气在线吗？"))
{
document.cookie="bookmarkit=yes"
JSAddFavorite()
}
}
}